A spindle unit used for a miniature motor or miniature rotor is conventionally formed as shown in FIG. 15.
That is to say, a pair of radial ball bearings 21 and 22 are arranged above and below on the outer periphery of a shaft 20, a cylindrical spacer 23 is arranged between outer races 21a and 22a of these radial ball bearings 21 and 22 to position the radial ball bearings 21 and 22 with each other, these members are fixed within a hole H of a bearing housing 24, such rotor 25 as a pulley, disc or turntable is fixed to the end of the shaft 20 and the shaft 20 side has been made rotatable.
The rotary mechanism of such roller as a conventional tape guide roller has been formed also of the same radial ball bearings.
However, in the above mentioned construction, sealing members S are arranged on both sides of balls 21c provided within the radial ball bearings 21 and 22 in order to prevent dust or the like from entering the radial ball bearings 21 and 22 and reducing the performance of the rotary mechanism, that is, a so-called double sealing structure is used. These radial ball bearings 21 and 22 are deficient in that the component parts are many, the assembly is complicated and the cost is high.
There is also the disadvantage that the clearance (in four places) of the radial ball bearings 21 and 22 cause a rotary vibration of the shaft 20.